Power-modulator for radiotransmission



H. D. ARNOLD.

POWER MODULATOR FO-R RADIOTBANSMISSION. APPLICATION FIL ED NOV 4,1916.

1,375,481, Patented Apr. 19, 1921.,

//4 1/21) for: Haro/d Q A //7 0/.

Continuation of application Serial No.

To all wlzom it may concern:

Be it known that I, HAROLD FOREST ARNOLD, a citizen of the United States, residing at East Orange, in the county of Essex and State of New Jersey, have invented certain new and useful Improvements in Power-Modulators for Radiotransmis sion, of which the following is a full, clear, ('OllClSQ, and exact description.

An object of this invention is to provide methods and means for modulating the high frequency power used for radio telegraphy or telephony in accordance with the signals to be transmitted, and to accomplish this result with a minimum of distortion and without requiring the passage of heavy currents directly through the telephone transmitter or other signaling device.

It has previously been proposed to effect the modulation by variably impeding the currents supplied by a high frequency alternating current source of powerthe alternating currentsource being in the output circuit of a. thermionic device on the input circuit of which is impressed audio frequency electromotive forces. The thermionic impedance is varied in accordance with the audio frequency electromotive force applied to the grid in the input circuit of the thermionic device.

This invention, however, while securing modulation of the output of any high frequency machine by the use of thermionic de vices, makes use of a novel and improved method of controlling the input circuit of the thermionic devices. In contradistinction to previous methods the present method.

impresses on the input members radio frequency electromotive forces modified in amplitude or in phase in accordance with speech. The radio frequency waves supplied to the input members are derived from the high frequency machine whose outputisto be modulated.

The radio frequency electromotive force applied to the input members varies the impedance of the thermionic device to the electromotive force of the same radio frequency output circuit to produce a modulated radio frequency current. Since the same radio frequency is applied to the thermionic input and Specification of Letters Patent.

output circuits, the wave form of the modulated high frequency mama Apr. 19, 1921..

46,842, filed August 23, 1915. This application filed November 4, 1916. Serial No. 129,470.

current in the output circuit is obtained with a minimum of distortion.

The impedance of the input circuit of the thermionic modulator is so high that substantially no current flows therein when an electromotive force is applied to its grid. The microphone or other transmitter which controls the modulating electromo'tive force applied tothe grid, need handle only a small amount of current and power as it has onl to determine the voltage applied to the gridi This application is a continuation of the application 'of Arnold, Serial No. 16,842, filed August 23, 1915, power modulator for radio transmission.

Referring to the drawings, Figures 1, 2 and 3 show diagrammatically three different systems embodying the invention.

In Fig. 1, 1 represents any suitable source of high frequency oscillations which are to be modulated in accordance with signals, and to be radiated. Connected between one terminal of the generator 1 and the line 21, is an inductance 2. The other terminal of the generator is connected to the line 22. Bridged across the lines 21 and 22 are one or more sets of oppositely connected thermionic devices 31 and 32, etc., which provide paths for. both half waves of the current from generator 1. It is necessary to provide two thermionic devices 31 and 32, connected in opposition, since each device is essentially unilaterally conducting. Inductively connected to the inductance 2 is an inductance 3, which forms part of the antenna system, 5, 3, 6, for radiating high frequency oscillations. Thermionic amplifier 31 having its output terminals in circuit ator l and inductance 2 has two plates 7 and 8 connected by a common terminal to line 21, two grids 9 and 10 connected by a common terminal to the line 23 and the heated filament 11 connected to the line 22. The thermionic devices 31 and 32 are oppositely connected to the lines 21 having its plates 7 8. connected to the line 22, the grids 9', 10 connected to line 24, and the filament 11' connected to line 21. Since the two oppositely connected devices 31 and 32 are provided, both half waves from the generator 1 will be transmitted.

In orderto vary the internal impedance between the output terminals z'. e., the heatand 22device 32- inductance 12, and resistance 13. Induc-.

the inductance 12 is the tively related to coil 14, in series with which isthe modulating transmitter 15, coil 16, condenser 17 and a portion of resistance 13 which is determined by the position of the adjustable contact 18. The relatively adjustable coils 12 and 14 and the adjustable resistance 13 comprise a phase shifting device by means of which the voltage applied to the grids may be given a proper phase with respect to the generator voltage supplied in the output circuits of the thermionic devices. Inductively related to the coil 16 is the coil 19, by means of which modulated high frequency oscillations are supplied to the line 23 and to the grids connected to this line. By means of the battery 41 the grids such as 9 and 10, connected to line 23, are maintained at a suitable negative potential. The coil 20 inductively related to the coil 16 supplies a voltage 180 out of phase from the voltage supplied by coil 19. The coil 20 supplies modulated oscillations to the line 24 and to the grids 9' and 10, the potential of which is maintained negative by means of the battery 42.

The operation of the device is as follows: A relatively small amount of high frequency energy is transferred by means of the coils 12 and 14 into the circuit 13, 14, 15, 16, 17 and 18 which may be tuned to the frequency of the generator. Under this condition, the current flowing in the circuit 13, 14, 15, 16, solely upon the resistance and will be extremely sensitive thereto. Any variations produced in the resistance of the transmitter 15, by speech or other means, produces a marked effect upon the current flowing in this circuit, and therefore a corresponding effect upon the high frequency potential applied to the grids 9, 10 and 9', 10'. This variation in the high frequency potential applied to the grids produces a like effect upon the impedance of the generator circuit through which the total output power must circulate. Consequently this output power is modulated in accordance with the signals impressed upon the microphone 15. In Fig. 2, the circuit including the coil 12 and resistance 13, instead of being directly connected to the generator as in Fig. 1, is

inductively related by means of coil 48 to 17 and 18 will depend the coils 2 and 3. As in Fig. 1, it is obvious I The third branch circuit passes through the thermionic devices. 'Variations in resistance of the transmitter element 15 change the high frequency current in the transmitter circuit and the electromotive forces applied to the Input circuits of the thermionic devices. The resulting variations in impedance of devices 31 and 32 determine the proportion of the current supplied by generator 1 which passes through these devices. The value of the portion of the current of generator 1 passing through coil 2 is therefore controlled by transmitter element 15.

Although this invention has been descr bed as especially applicable to radio signalmg, it is obvious that it may be applied to s stems of wire transmission.

hile I have illustrated and described the features of my invention in connection with several specific transmitting circuits, it is to be understood that the invention is not limited to the systems illustrated, but may be embodied in such otherconstructions or circuit arrangements as come within the scope of the appended claims.

What is claimed is: Y

1. The method of transmission which conslsts in variably impeding a pulsating electron stream in accordance with modulated radio frequency waves to produce a modulated current and transmitting the electrical energy of said current to a distant station.

2. The method of'transmission which consists m variably impeding a pulsating electron stream in accordance with modulated radio frequency waves having lower frequency amplitude variations to produce modulated; oscillations.

l 3. The method of transmission which conslsts 1n variably impeding a pulsating electron stream in accordance with modulated radio frequency waves having lower frequency amplitude variations to roduce modulated current, and transmitting the energy of said current to a work circuit.

4. The method of modulation which conslsts in variably impeding in accordance with modulated radio frequency waves havmg lower frequency amplitude variations, a pulsating electron stream which periodically falls to zero value.

5. An electric system including a constantly conductive dischargev device having input and output circuits, means for supweasel plying modulated radio frequency oscillations having amplitude variations of lower frequency to said input circuit, and means connected to said discharge device for supplying pulsating space current.

6. The method of modulation which consists in variably impeding electron streams of opposite phase in accordance with modulated radio frequency waves.

7. The method of signaling which consists in supplying electron streams of opposite phase from a radio frequency source, modulating radio frequency waves controlled by said source, and in variably impeding said electron streams in accordance with said modulated waves.

8. A signaling system comprising a thermionic device having input and output circuits and a constantly active source of electrons, means for supplying modulated radio frequency waves having amplitude variations of lower frequency to said input circuit, and means for impressing an alternating electromotive force upon said output circuit.

9. In a high-frequency signaling system, a generator circuit containing a generator of high-frequency oscillations, a vacuum tube device having a cathode and an impedance controlling element associated therewith, and means for impressing modulated high-frequency oscillations of low power on a circuit connecting said cathode and said impedance controlling element to modify the impedance of said device and generator circuit in accordance with signals to -.be transmitted.

' 10. In a high-frequency signaling system, a thermionic device havmg an output circuit, a generator of high frequency oscillations associated therewith for supplying the space current in said output circuit, a circuit deriving a relatively small amount of.

power of said high frequency from the generator, means for modulating said high fre-' quency power, and means for causing said modulated high frequency power to vary the impedance of the device associated with the generator.

11. In a high-frequency signaling system,

a enerator circuit containing a generator of high-frequency oscillations, a thermionic device of the audion type associated therewith and deriving its space current therefrom, a circuit associated with the generator for deriving a relatively small amount of high-frequency power therefrom, a signaling device for modulating said power, and means including an inductive coupling between said last named circuit and an impedance control circuit of said thermionic device for varying the impedance of the generator circuit in accordance with said signal modulated high frequency power.

12. In a high-frequency signaling system, a generator circuit containing a generator of high-frequency oscillations, a thermionic device of the audion type associated therewith, a circuit associated with and comprising means for tuning the same to the frequency of the generator for deriving a relatively small amount of high-frequency power therefrom, and a telephone transmit ter in said tuned circuit for modulating said power, said tuned circuit comprising means for inductively connecting the same to the input circuit of said device, whereby the impedance of the generator circuit is modulated in accordance with the variations in the transmitter,

13. In a high-frequency signaling system, a generator circuit containing a gen erator of high-frequency oscillations, thermionic means of the audion type in series therewith, a-circuit inductively associated with and comprising means for tuning the same to the frequency of the generator for deriving a relatively small amount of high-. frequency power therefrom, and a telephone transmitter in said tuned circuit for modulating said power, said tuned circuit comprising means for inductively connecting the same to the input circuit of the thermionic means, whereby the impedance of the generator circuit is modulated in accordance with the variations in the transmitter. In witness whereof, I hereunto subscribe my name this 2nd day of November A. D.,

HAROLD D. ARNOLD. 

